stereo preamp from mp3 to roland micro cube.???

[deadastronaut]

hi guys i have a roland micro cube i take camping etc...i took it camping along with my mp3 player as it has an AUX in...

but...my mp3 was very very quiet, ....so i guess i need a preamp for it...which would come in handy anyway, as sometimes my missus plugs her laptop into it and i can then control the volume instantly..

now on the roland there is no AUX IN  volume control.......its  set  to be controlled externally (by mp3/laptop volumes)...which is a nightmare as my missus plays music videos a lot, with varying volume levels arghhhhhh...

so..

has anyone got a nice/easy portable low power stereo preamp circuit with summing volume so i can instantly turn the bugger down/up...and have my mp3's loud so i can jam along with my backing tracks and annoy rabbits etc...thanks guys!.

[artifus]

maybe here? http://beavishifi.com/

[deadastronaut]

cheers art...will these run on a single 9v battery though?..

[artifus]

not checked that site out in a while - your post reminded me of it. there's prolly better solutions out there. jfet requires 2 pp3 and the tranny none what so ever.

*and thanks for the reminder - transformer article links to an excellent prr post*

[deadastronaut]

how about this...looks ideal with the summing vol too...

http://audiocircuit.blogspot.co.uk/2011/11/hi-fi-audio-amplifiers-with-tl072.html

the bottom one..

[artifus]

many ways to crack this nut. i s'pose your biggest concern in this scenario is current consumption due to battery life. my initial thought with the transformer suggestion was lack of power but am unsure as to the drain it may or may not demand from source. maybe just a vol pot or bypass switch for your two source levels could be added. i don't speak math well enough to comment on power consumption.

*your cube will do the summing for you*

[deadastronaut]

cheers man,  yeah i need it to run on 9v , and just have an overall volume control on it...

a simple opamp/or tranny one will be fine... that transformer one looks cool..no power etc...but i just want to make one out of common bit that i have already..

[Ronan]

A dual opamp TLC2262 with vol knob but no "on" LED, and the 9V battery will last for a year or so, build it into a small pedal box. Perfect for camping and portability. Yeah I know you like LED's, maybe put a mini solar panel on it to charge a NiMh batt...

[deadastronaut]

cheers ian..i want to make it out of parts i have at the mo though...

how about 2 of these?..i have an old penfold book with something very similar..

http://www.youtube.com/watch?v=9SclQIWkOtk&feature=related

skip to 2:57

[deadastronaut]

and this?.

http://www.electronicecircuits.com/electronic-circuits/741-stereo-preamplifier-circuit-diagram

[Ronan]

Go for the first one, the tranny one. That should be fine for your purpose.

[deadastronaut]

cheers ian...yep looks nice and simple...i'll knock up a vero/pcb of it...

[deadastronaut]

one question on that though

in the video he has a 10k from v to input that he says omit if not using as a mic blah.... so can i just leave that connection off....i'e from v to input..?..

or should i still connect the v to the input with no resistor?...

http://www.youtube.com/watch?v=9SclQIWkOtk&feature=related

[artifus]

electret mics are basically fets - the resistor provides bias for that fet so may be omitted.

*info* http://www.epanorama.net/circuits/microphone_powering.html if you have any of these little mics knocking about they are worth playing with and can provide a reasonable response - check the simplest circuit which is a capsule, resistor and xlr connector. i've made a few and quality depends on individual capsule, even from the same batch, but playing with resistor value can provide a quiet (noise wise) and decent signal comparable to cheap small diaphragm b*ringers, etc. over short cable runs. handy in an emergency.

[deadastronaut]

cheers art:

i just breadboarded one transistor channel as above (video)and put my mp3 through it (full vol)into my roland...its still very quiet...

edit:  i just swapped the 100k for a  50k trim...much better..back in a bit...i'll tinker..

[Ronan]

This cct will do the job with less parts, and probably a lot better.



The 10K input resistor and 50K pot determine max gain - 50/10 = 5x gain max. You can use 1k input resistor and 5K pot, or 100K resistor and 500K pot, whatever you have lying around, not critical. With the pot turned right down it will actually decrease gain to less than unity, but not turn the music off completely, a by-product of minimum components to do the job I guess.

[artifus]

deano himself admits to being a hack - check his blog for comments as he is often corrected with suggested alternatives.

[Ronan]

In case you're wondering Rob, the circuit above should be capable of almost blowing pcb tracks off your microcube's line in circuit 
If you need more gain, make the input resistors smaller or the dual pot larger.

[deadastronaut]

@ian: cheers man i'll defo give that a go on bread now....and watch my roland explode..thanks man..

[Ronan]

Minor mod made to the input side, refresh browser...oops. Added 1uF input caps. May or may not cause grief.